With reference to the existing technology, ultraviolet light is widely used in detection/purification/sterilization apparatus. In these apparatus, the intensity of the UV light passing through water or any other liquid, is detected at the reactor wall of the apparatus and compared with a known intensity of the UV light generated by an UV lamp. To detect the intensity of the UV light, normally an electronic UV sensor and an appropriate power arrangement, especially an external power source, are necessary. However, the UV sensor and the power arrangement are costly and inconvenient in terms of use and maintenance. There is a need to mitigate, even overcome, the drawbacks of the current UV sensor systems.